Novel polymeric co-initiators

ABSTRACT

A novel polymeric co-initiator is disclosed comprising a dendritic polymer core with at least one co-initiating functional group as an end group. The polymeric co-initiators are useful in radiation curable compositions such as varnishes, lacquers and printing inks and are especially useful in radiation curable inkjet inks. The dendritic polymeric core is preferably a hyperbranched polymer.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/601,886 filed Aug. 16, 2004, which is incorporated by reference. Inaddition, this application claims the benefit of European ApplicationNo. 04103395.2 filed Jul. 15, 2004, which is also incorporated byreference.

TECHNICAL FIELD

The present invention relates to novel polymeric co-initiators, usefulin radiation curable compositions such as varnishes, lacquers andprinting inks, e.g. radiation curable inkjet inks.

BACKGROUND ART

Commercial radiation curable inkjet inks generally contain significantamounts of low molecular weight co-initiators, such asethyl-4-dimethylaminobenzoate or N-methyl-diethanolamine. Thisco-initiator is used in combination with a Norrish type II-initiator toaccelerate the radiation curing process. No problem arises if all of theco-initiator is consumed and built into the polymeric network. However,hydrogen transfer from the co-initiator to the Norrish type II-initiatoris rarely quantitative, resulting in unreacted co-initiator. In foodpackaging printed upon with a radiation curable composition, thisunreacted co-initiator remains mobile and if toxic will cause healthrisks upon being extracted into the food. Unreacted co-initiators arealso known to adversely affect the physical properties of the packagingmaterial.

One approach in solving these problems is to design co-initiators with ahigher molecular weight.

JP 2000086713 (TOYO INK) discloses the use of the reaction product of anunsaturated monomer bearing (meth)acryloyl groups or vinyl ether groupshaving an number average molecular weight of more than 500 with aprimary or secondary amine as co-initiator in radiation curablecompositions. However, using this approach only co-initiators with lowfunctionality can be obtained.

EP 434098 A (UNION CARBIDE) discloses the use of amino terminatedpolyoxyalkylenes as co-initiators in radiation curable compositions. Theclaimed polyoxyalkylenes also have a low functionality, requiring theuse of large amounts of unreactive polymer in the matrix compared to lowmolecular weight co-initiators.

The combination of a co-initiator and an initiator in a conventionallinear polymer geometry has been described by ANGIOLINI, et al.Polymeric photoinitiators based on side-chain benzoin methyl ether andtertiary amine moieties for fast UV-curable coatings. Polymers forAdvanced Technologies. 1993, vol.4, no.6, p. 375-384. Althoughpotentially interesting to reduce extractable residues, the lineargeometry of the polymer increases the solution viscosity of theformulations to an undesirable level for a great number of applicationswith radiation curable compositions, e.g. inkjet inks and lacquers.

WO 9907746 (DSM) discloses a radiation-curable resin compositioncontaining at least a radiation-curable resin, a photo-excitablecompound and an aliphatic amine, characterised in that as amine ischosen a compound containing at least one tertiary amino group, at leastone substituent of the tertiary amino group being an aliphatic chaincontaining at least one electron-withdrawing group, excluding the casewhere the aliphatic amine consists of one tertiary amine group with thealiphatic chain being a cyanoethyl group and the other two substituentsof the tertiary amino group forming part of an alkyl ring with 4 or 5carbon atoms.

In a preferred embodiment and in all of the examples,Astramol™-dendrimers, commercially available from DSM, are used asco-initiator in comparison with low molecular compounds. However, thelow generation dendrimers are in fact low molecular weight compounds,while higher generations require laborious synthetic work, making themtoo expensive for several applications. A further derivatization ofthese compounds to compatibilize them with different radiation curablecompositions is impossible. The same Astramol™-dendrimers are describedin WO 9903930 (DSM) in combination with maleimides as initiator.

WO 0222700 (PERSTORP SPECIALTY CHEM) discloses a radiation curabledendritic oligomer or polymer, characterised in that the radiationcurable dendritic oligomer or polymer normally has at least one terminalgroup of Formula (A):

and normally at least one terminal group of Formula (B):

wherein R1 and R2 individually are hydrogen or methyl and wherein R3 andR4 individually are alkyl, aryl, alkylaryl, arylalkyl, alkylalkoxy,arylalkoxy, said alkyl and/or said aryl optionally having one or morehydroxyl groups. The dendritic polymers are claimed to be of particularof interest for curing under air compared to conventional curabledendritic oligomers. However, these oligomeric co-initiators tend tolose their effectiveness when coupled to a polymer, which does notcontain acrylates, as stated in DAVIDSON, Stephen R. Exploring theScience Technology and Applications of UV and EB-curing. LONDON, UK:SITA Technology Ltd, 1999. p. 141. and DAVIDSON, Stephen R., et al. TypeII polymeric photoinitiators (polyetherimides) with built-in aminesynergist. Journal of Photochemistry and Photobiology, A: Chemistry.1995, vol.91, no.2, p. 153-163.

There is therefore a need to provide cheap, effective co-initiatorssuitable for radiation curable compositions for use on food packagingwith these co-initiators not being extractable into food or adverselyaffecting the physical properties of the packaging material. Theco-initiator should be easy to manufacture and should be compatible witha wide range of radiation curable compositions without causing highsolution viscosity.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a new class of veryeffective polymeric co-initiators.

It is a further object of the present invention to provide a new classof polymeric co-initiators that are easy to manufacture and can beeasily made compatible with a wide range of radiation curablecompositions.

It is also an object of the present invention to provide a radiationcurable composition comprising at least one of this new class ofpolymeric co-initiator compatible with a wide range of radiation curablecompositions.

It is also an object of the present invention to provide a radiationcurable inkjet ink comprising at least one of this new class ofpolymeric co-initiator according to the present invention that issuitable for inkjet printing on food packaging.

These and other objects of the invention will become apparent from thedescription hereinafter.

SUMMARY OF THE INVENTION

It was surprisingly found that polymeric co-initiators with a specificmolecular geometry are at least as effective as their low molecularweight counterparts, making them especially useful for radiation curableformulations having lower amounts of extractable residues. Although thepolymeric co-initiators have a high functionality, they exhibit alimited influence on viscosity.

Objects of the present invention are realized with a polymericco-initiator comprising a dendritic polymer core with at least oneco-initiating functional group as an end group.

The objects of the present invention are also realized with a radiationcurable composition containing a polymeric co-initiator comprising adendritic polymer core with at least one co-initiating functional groupas an end group.

The objects of the present invention are also realized with an inkjetink containing a polymeric co-initiator comprising a dendritic polymercore with at least one co-initiating functional group as an end group.

The objects of the present invention are also realized with a processfor manufacturing a polymeric co-initiator, comprising the steps of:

-   -   a) providing a dendritic polymer core, and    -   b) attaching at least one co-initiator or co-initiator        derivative to said dendritic polymer core as an end group.

Further advantages and embodiments of the present invention will becomeapparent from the following description.

DETAILED DESCRIPTION OF THE INVENTION DEFINITIONS

The term “actinic radiation” as used in disclosing the presentinvention, means electromagnetic radiation capable of initiatingphotochemical reactions.

The term “ultraviolet radiation” as used in disclosing the presentinvention, means electromagnetic radiation in the wavelength range of 4to 400 nanometers.

The term “UV” is used in disclosing the present application as anabbreviation for ultraviolet radiation.

The term “co-initiator” as used in disclosing the present invention,means any molecule capable of transferring a hydrogen to the excitedstate of a Norrish type II-initiator and initiating the radicalpolymerization of a radiation curable composition.

The term “Norrish type II-initiator” as used in disclosing the presentinvention, means a photoinitiator which is activated by actinicradiation and forms free radicals by hydrogen abstraction or electronextraction from a second compound that becomes the actual initiatingfree radical.

The term “branched polymer” as used in disclosing the present invention,means a polymer chain having branch points that connect three or morepolymeric chain segments.

The term “DB” is used in disclosing the present application as anabbreviation for degree of branching.

The term “dendritic polymer” as used in disclosing the presentinvention, comprises dendrimers and hyperbranched polymers.

The term “hyperbranched polymer” as used in disclosing the presentinvention, means a polymer having a plurality of branch points andmultifunctional branches that lead to further branching with polymergrowth. Hyperbranched polymers are obtained by a one-step polymerizationprocess and form a polydisperse system with varying degrees of branching(DB<100%).

The term “dendrimers” as used in disclosing the present invention, meanswell-defined monodisperse structures in which all branch points are used(DB=100%). Dendrimers are obtained by a multi-step synthesis.

The term “functional group” as used in disclosing the present invention,means an atom or group of atoms, acting as a unit, that has replaced ahydrogen atom in a hydrocarbon molecule and whose presence impartscharacteristic properties to this molecule.

The term “low functionality” as used in disclosing the presentinvention, means having not more than five functional groups.

The term “end group” as used in disclosing the present invention, meansthe terminal group on a branch. In the case of a dendrimer orhyperbranched polymer, a plurality of end groups is present.

The term “co-initiating functional group” as used in disclosing thepresent invention, means a functional group that renders the moleculecapable of functioning as a co-initiator.

The term “colorant”, as used in disclosing the present invention, meansdyes and pigments.

The term “dye”, as used in disclosing the present invention, means acolorant having a solubility of 10 mg/L or more in the medium in whichit is applied and under the ambient conditions pertaining.

The term “pigment” is defined in DIN 55943, herein incorporated byreference, as an inorganic or organic, chromatic or achromatic colouringagent that is practically insoluble in the application medium under thepertaining ambient conditions, hence having a solubility of less than 10mg/L therein.

The term “alkyl” means all variants possible for each number of carbonatoms in the alkyl group i.e. for three carbon atoms: n-propyl andisopropyl; for four carbon atoms: n-butyl, isobutyl and tertiary-butyl;for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyland 2-methyl-butyl etc.

The term “acyl group” as used in disclosing the present invention means

-   -   —(C═O)-aryl and —(C═O)-alkyl groups.

The term “aliphatic group” as used in disclosing the present inventionmeans saturated straight chain, branched chain and alicyclic hydrocarbongroups.

The term “aryl group” as used in disclosing the present invention meansan assemblage of cyclic conjugated carbon atoms, which are characterizedby large resonance energies, e.g. benzene, naphthalene and anthracene.

The term “alicyclic hydrocarbon group” means an assemblage of cyclicconjugated carbon atoms, which do not form an aromatic group, e.g.cyclohexane.

Dendritic Polymers

The polymeric co-initiator according to the present invention contains acore of dendritic polymer, e.g. a dendrimer or a hyperbranched polymer.The polymeric co-initiator according to the present invention haspreferably a core of hyperbranched polymer.

Dendrimers are characterized by cascade-type branching, i.e. abranch-on-branch topology. Dendrimers are prepared in a multi-stepsynthesis, based on repeated branching and deprotection schemes asdisclosed by NEWCOME, G. R., et al. Dendritic Molecules: Concepts,Synthesis, Perspectives. VCH: WEINHEIM, 2001. Dendrimer synthesisstrategies generally aim at fully branched polymers, although inrecently reported examples a fraction of imperfectly branched specieshas been reported as (undesired) side-products. Suitable dendrimers arepolyamidoamine (PAMAM) Starburst™ dendrimers as disclosed by TOMALIA, etal. A new class of polymers: starburst-dendritic macromolecules. Polym.J. 1985, vol.17, p. 117. and convergently prepared polybenzyletherdendrimers as disclosed by HAWKER, et al. Preparation of polymers withcontrolled molecular architecture. A new convergent approach todendritic macromolecules. J. Am. Chem. Soc. 1990, vol.112, p. 7638.

Synthesis

The stepwise preparation, which represents the only strategy for thepreparation of dendrimers at present, is a limiting factor for mostapplications. In contrast to dendrimers, the structurally irregular, i.e. hyperbranched polymers are obtained in a single synthetic step.

In the present invention both polymers obtained by strict hyperbranchingpolymerization as well as polymers obtained by subcriticalpolymerization of e.g. A₂+B₃ types of monomers are considered ashyperbranched.

A stringent criterion for strict hyperbranching polymerization is thatno critical conversion p_(c) may exist, at which gelation of the systemoccurs and a network structure is obtained, as disclosed by BURCHARD, W.Solution properties of branched macromolecules. Advances in PolymerScience. 1999, vol.143, no. 1, p. 113-194.

Hyperbranched materials can thus be obtained by polycondensation of AB₂or AB_(m)-type monomers with complementary functionality's A and B, theonly coupling reaction in the system being the linking of A and B.Details on this type of polyfunctional polycondensation are disclosed byFLORY, P. J. Molecular size distribution in three-dimensional polymers.VI.

Branched polymer containing A-R-Bf-1-type units. Journal of the AmericanChemical Society. 1952, vol.74, p. 2718-2723.

U.S. Pat. No. 4,857,630 (DU PONT) and KIM, Y. H., et al. Hyperbranchedpolyphenylenes. Polymer Preprints (American Chemical Society, Divisionof Polymer Chemistry). 1988, vol.29, no.2, p. 310-311. disclosesynthesis methods for preparing hyperbranched polyphenylenes.

Methods for preparing hyperbranched polymers based on polycondensationof AB₂-monomers are further disclosed in U.S. Pat. No. 5,196,502(KODAK), U.S. Pat. No. 5,225,522 (KODAK) and U.S. Pat. No. 5,214,122(KODAK).

Another suitable approach for preparing hyperbranched polymer structuresis the polymerization of linear AB*-type inimers. Inimers are compoundsthat possess a common, linearly polymerizable moiety, such as a vinylgroup or a strained cyclic component as well as an initiating group inthe same molecule. Cyclic inimers have been used in the preparation ofhyperbranched structures by VANDENBERG, E. J. Polymerization of glycidoland its derivatives: a new rearrangement polymerization. Journal ofPolymer Science. 1985, vol.23, no.4, p. 915-949., FRECHET, J.Self-condensing vinyl polymerization: an approach to dendriticmaterials. Science (Washington, D.C.). 1995, vol.269, no.5227, p.1080-1083. and EP 791021 A (CORNELL RES FOUNDATION INC).

Linear AB type compounds, commonly called “linear co-monomers” as wellas poly-B-functional compounds of B_(f)-structure may be present,commonly designated “core molecules”. An overview of the structuralpossibilities as well as a stringent definition for the degree ofbranching DB, a relevant parameter for the functionality ofhyperbranched polymers is disclosed by HOLTER, D., et al. Degree ofbranching in hyperbranched polymers. Acta Polymerica. 1997, vol.23,no.48, p. 30-35., HOLTER, E. J., et al. Degree of branching (DB) inhyperbranched polymers. Part 2. Enhancement of the DB. Scope andlimitations. Acta Polymerica. 1997, vol.48, no.8, p. 298-309. and FREY,H., et al. Degree of branching in hyperbranched polymers. Part 3.Copolymerization of ABm monomers with AB and ABn monomers. Journal ofPolymer Science. 1999, vol.50, no.2-3, p. 67-76.

The state of the art in hyperbranched polymer research has been reviewedin:

-   -   (a) JIKEI, M. Hyperbranched polymers: a promising new class of        materials. Progress in Polymer Science. 2001, vol.26, no.8, p.        1233-1285.    -   (b) NEWCOME, G. R., et al. Dendritic Molecules: Concepts,        Synthesis, Perspectives. VCH: WEINHEIM, 2001.    -   (c) KIM, Y., et al. Hyperbranched polymers 10 years after.        Journal of Polymer Science, Part A: Polymer Chemistry. 1998,        vol.36, no.11, p. 1685-1698.    -   (d) VOIT, B., et al. New developments in hyperbranched polymers.        Journal of Polymer Science, Part A: Polymer Chemistry. 2000,        vol.38, no.14, p. 2505-2525.    -   (e) SUNDER, A., et al. Controlling the growth of polymer trees:        concepts and perspectives for hyperbranched polymers.        Chemistry—A European Journal. 2000, vol.6, no.14, p. 2499-2506.

From these reviews, it is evident that hyperbranched polymers areclearly distinguishable from the regularly branched dendrimers as wellas from branched structures based on A₂+B₃ polymerization of twopolyfunctional monomers that inevitably leads to gelation, i.e. networkformation, if polymerization is not stopped at a subcritical level.

Hyperbranched polymers commonly possess broad molecular weightdistribution. The polydispersity M_(w)/M_(n) is usually greater than 5and more often greater than 10. Recently new concepts have beenintroduced that are based on the slow addition of AB₂ or latent AB₂monomers of suitable reactivity to a polyfunctional (B_(f)) coremolecule. The procedure is disclosed by RADKE, W., et al. Effect ofCore-Forming Molecules on Molecular Weight Distribution and Degree ofBranching in the Synthesis of Hyperbranched Polymers. Macromolecules.1998, vol.31, no.2, p. 239-248. and HANSELMANN, R., et al. HyperbranchedPolymers Prepared via the Core-Dilution/Slow Addition Technique:Computer Simulation of Molecular Weight Distribution and Degree ofBranching. Macromolecules. 1998, vol.31, no.12, p. 3790-3801.

Hyperbranched Polymer Core

The size of the hyperbranched polymer core for a polymeric co-initiatoraccording to the present invention is determined by the selectedapplication. Most inkjet applications require inkjet inks with a lowviscosity, usually lower than 100 mPa.s. Hence for inkjet applications,the hyperbranched polymers preferably have a M_(w) smaller than 100,000,more preferably smaller than 50,000 and most preferably smaller than20,000.

The hyperbranched polymer core for a polymeric co-initiator according tothe present invention is preferably obtained by the method of slowmonomer addition. This results in a narrow polydispersity of thehyperbranched polymers. Particularly preferred in the present inventionare hyperbranched polymers with a polydispersity M_(w)/M_(n) smallerthan 3.

Suitable hyperbranched polymer cores are disclosed in GAO, C., et al.Hyperbranched polymers: from synthesis to applications. Progress inPolymer Science. 2000, vol.29, no.3, p. 183-275.

Other suitable hyperbranched polymer cores are given in Table 1, withoutbeing limited thereto. TABLE 1 PC-1

PC-2

PC-3

PC-4

PC-5

PC-6

PC-7

PC-8

The hyperbranched polymer core can be used as a core for terminalgrafting before derivatization with a reactive co-initiator(derivative). This yields a hyperbranched multiple arm graft starcopolymer, which is also considered to be a hyperbranched polymer coreaccording to the present invention. Suitable examples of this type ofpolymers are disclosed in SUNDER, A., et al. HyperbranchedPolyether-Polyols Based on Polyglycerol: Polarity Design by BlockCopolymerization with Propylene Oxide. Macromolecules. 2000, vol.33,no.2, p. 309-314. and MAIER, S., et al. Synthesis ofpoly(glycerol)-block-poly(methyl acrylate) multi-arm star polymers.Macromolecular Rapid Communications. 2000, vol.21, no.5, p. 226-230.

Any hyperbranched polymer can be used as a polymer core in the polymericco-initiators, but hyperbranched polyglycidols or hyperbranchedcopolymers of glycidol and other epoxides are particularly preferred.They can be readily prepared with a narrow molecular weight distributionin a single step procedure from commercially available monomers over abroad range of molecular weights. The reaction of these core polymerswith at least one co-initiator or co-initiator derivative yields aparticularly preferred class of hyperbranched polymeric co-initiatorsaccording to the present invention.

Branched polyols based on glycerol units are usually prepared byreacting glycidol with a hydrogen-containing compound (e.g., glycerol)in the presence of inorganic acids as disclosed by JP 61043627 A (DAICELCHEM IND.) or organic acids as disclosed by JP 58198429 A (NIPPON YUSHI)as catalyst. The polymerization of glycidol can also be achieved viacationic polymerization using cationic initiators, such as BF₃ asdisclosed by TOKAR, R., et al. Cationic polymerisation of glycidol:coexistence of the activated monomer and active chain end mechanism.Macromolecules. 1994, vol.27, p. 320. and DWORAK, A., et al. Cationicpolymerization of glycidol. Polymer structure and polymerizationmechanism. Macromolecular Chemistry and Physics. 1995, vol.196, no.6, p.1963-1970. However, a cationic polymerization method leads tohyperbranched polymer with a polydispersity larger than 3 and molecularweights can not be controlled.

A suitable procedure for the preparation of hyperbranched polyglycerolswith a controlled molecular weight is disclosed in DE 19947631 A(BAYER). This is achieved by adding glycidol diluted in a hydrocarbon oran ether to a suitable polyol initiator that is dissolved in diglyme oranother hydrocarbon as disclosed in SUNDER, A., et al. ControlledSynthesis of Hyperbranched Polyglycerols by Ring-Opening MultibranchingPolymerization. Macromolecules. 1999, vol.32, no.13, p. 4240-4246. Themonomer is added as solution containing between 20 and 99.9 wt %, e.g.,60%-90% THF. Full incorporation of an initiator is promoted by the useof a polyfunctional initiator.

Co-Initiators

A polymeric co-initiator according to the present invention comprises adendritic polymer core with at least one co-initiating functional groupas an end group. It is essential that the co-initiating functional groupis present as an end group on the polymer core. A co-initiatingfunctional group present in the core of the polymeric structure loosesit effectiveness due to steric reasons.

The polymeric co-initiators are obtained by reaction of at least oneco-initiator or co-initiator derivative and a dendritic polymer core.Preferably, the polymeric co-initiators have at least five co-initiatingfunctional groups as end groups on the dendritic polymer core, and mostpreferably at least 7 co-initiating functional groups as end groups.

Any co-initiator or co-initiator derivative known in the prior art canbe used. A preferred co-initiator or co-initiator derivative forcreating the co-initiating functional group on the dendritic polymercore is selected from the group consisting of an aliphatic amine, anaromatic amine and a thiol. Tertiary amines, heterocyclic thiols and4-dialkylamino-benzoic acid derivatives are particularly preferred.

Suitable co-initiators according to the present invention, which can beattached as a co-initiating functional group to the polymer core, aregiven in Table 2 without being limited thereto. TABLE 2 SYN-1

SYN-2

SYN-3

SYN-4

SYN-5

SYN-6

SYN-7

SYN-8

SYN-9

SYN-10

SYN-11

SYN-12

SYN-13

SYN-14

SYN-15

The dendritic polymer core can be fully or partially derivatized.

It is evident for those skilled in the art that many types ofderivatization chemistry can be used in the synthesis of the polymericco-initiators. In the case of hyperbranched polyglycidols,esterification and etherification is particularly preferred.

In a preferred embodiment, the polymeric co-initiators are furtherderivatized with a compatibilizing group. A compatibilizing group isdefined as a functional group making the polymeric co-initiator moresoluble in a specific radiation curable composition.

Suitable examples of polymeric co-initiators for use in a radiationcurable composition according to the present invention are given below,without being limited thereto. The structures given represent onemolecular weight with one degree of derivatization out of thedistribution found in each prepared sample. The structures represent amore generic structure, as a specific example for different molecularweights and degrees of substitution. It is obvious for those skilled inthe art that each polymer sample is a mixture of similar individualcompounds, differing in both molecular weight and degree of substitutionand that the chemistry can be extended over a wide range of molecularweights.

Suitable polymeric co-initiators according to the present invention havea hyperbranched polyether core. Example of a hyperbranched polyethercore:

Suitable polymeric co-initiators according to the present invention havea hyperbranched polyether core, as displayed above, to which aco-initiating functional group and optionally a compatibilizing groupcan be attached using the compounds displayed in Table 3, without beinglimited thereto. TABLE 3 Co-initiator R1—COOH Compatibilizer R2—COOHPE-1

PE-2

PE-3

PE-4

PE-5

PE-6

PE-7

Suitable polymeric co-initiators according to the present invention havea hyperbranched polyester core. Example of a hyperbranched polyestercore:

Suitable polymeric co-initiators according to the present invention havea hyperbranched polyester core, as displayed above, to which aco-initiating functional group and optionally a compatibilizing groupcan be attached using the compounds displayed in Table 4, without beinglimited thereto. TABLE 4 Co-initiator R1—X Compatibilizer R2—X PES-1

PES-2

PES-3

PES-4

PES-5

Suitable polymeric co-initiators according to the present invention havea hyperbranched polyamide core. Example of a hyperbranched polyamidecore:

Suitable polymeric co-initiators according to the present invention havea hyperbranched polyamide core, as displayed above, to which aco-initiating functional group and optionally a compatibilizing groupcan be attached using the compounds displayed in Table 5, without beinglimited thereto. TABLE 5 Co-initiator R1—COOH Compatibilizer R2—COOHPAM-1

PAM-2

PAM-3

PAM-4

PAM-5

Radiation Curable Composition

The polymeric co-initiator according to the present invention can beused in any radiation curable composition such as a varnish, a lacquerand a printing ink, and especially useful in radiation curable inkjetinks.

The radiation curable inkjet ink is preferably jetted on an ink jetrecording element chosen from the group consisting of paper, coatedpaper, polyolefin coated paper, cardboard, wood, composite boards,plastic, coated plastic, canvas, textile, metal, glasses, plant fibreproducts, leather, magnetic materials and ceramics.

The radiation curable inkjet ink jetted on an ink jet recording elementcreates an uncured printed image. This printed image is cured byradiation or electron beam exposure. A preferred means of radiationcuring is ultraviolet light.

Radiation-Curable Inkjet Ink

A radiation-curable inkjet ink contains at least three components: (i) aradiation-curable compound, (ii) a Norrish type II initiator, and (iii)a polymeric co-initiator according to the present invention. A preferredamount of the polymeric co-initiator is 1-50 wt % of the total inkweight, and more preferably 1 to 25 wt % of the total ink weight.

The radiation-curable compound can be selected from monomers and/oroligomers that can be polymerized by a curing means of an inkjetprinter.

The radiation-curable inkjet ink preferably further contains at leastone colorant, i.e. pigment or dye.

The radiation-curable inkjet ink may contain a polymerization inhibitorto restrain polymerization by heat or actinic radiation. It is preferredto add an inhibitor during preparation of the inkjet ink.

The radiation-curable inkjet ink may further contain at least one resinin order to obtain a stable dispersion of the colorant in the inkjetink.

The radiation-curable inkjet ink preferably further contains at leastone surfactant.

The radiation-curable inkjet ink preferably further contains at leastone solvent.

The radiation-curable inkjet ink preferably further contains at leastone biocide.

An inkjet printer generally uses a radiation-curable inkjet ink setconsisting of a plurality of radiation-curable inkjet inks.

Radiation-Curable Compounds

The radiation curable inkjet ink contains monomers and/or oligomers,which are polymerized by the curing means of the inkjet printer.

Monomers, oligomers or prepolymers may possess different degrees offunctionality, and a mixture including combinations of mono-, di-, tri-and higher functionality monomers, oligomers and/or prepolymers may beused. These components are curable, typically photo-curable, e.g. UVcurable, and should adhere to the ink-receiver surface after printingand serve to bind the colorant. A mixture of two or more monomers of thesame functionality is preferred. With particularly preferred a mixtureof two di-functional monomers.

The viscosity of the radiation curable inkjet ink can be adjusted byvarying the ratio between the monomers and oligomers.

Any method of conventional radical polymerization, photo-curing systemusing photo acid or photo base generator, or photo induction alternatingcopolymerization may be employed. In general, radical polymerization andcationic polymerization are preferred, and photo induction alternatingcopolymerization needing no initiator may also be employed. Furthermore,a hybrid system of combinations of these systems is also effective.

Cationic polymerization is superior in effectiveness due to lack ofinhibition of the polymerization by oxygen, however it is slow andexpensive. If cationic polymerization is used, it is preferred to use anepoxy compound together with an oxetane compound to increase the rate ofpolymerization. Radical polymerization is the preferred polymerizationprocess.

Any polymerizable compound commonly known in the art may be employed.Particularly preferred for use as a radiation-curable compound in theradiation curable inkjet ink, are monofunctional and/or polyfunctionalacrylate monomers, oligomers or prepolymers, such as isoamyl acrylate,stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate,isoamylstyl acrylate, isostearyl acrylate, 2-ethylhexyl-diglycolacrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethylhexahydrophthalicacid, butoxyethyl acrylate, ethoxydiethylene glycol acrylate,methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate,methoxypropylene glycol acrylate, phenoxyethyl acrylate,tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethylacrylate, 2-hydroxypropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate,vinyl ether acrylates such as described in U.S. Pat. No. 6,310,115(AGFA), 2-(vinyloxy)ethylacrylate, 2-acryloyloxyethylsuccinic acid,2-acryloyxyethylphthalic acid, 2-acryloxyethyl-2-hydroxyethyl-phthalicacid, lactone modified flexible acrylate, and t-butylcyclohexylacrylate, triethylene glycol diacrylate, tetraethylene glycoldiacrylate, polyethylene glycol diacrylate, dipropylene glycoldiacrylate, tripropylene glycol diacrylate, polypropylene glycoldiacrylate, 1,4butanediol diacrylate, 1,6hexanediol diacrylate,1,9nonanediol diacrylate, neopentyl glycol diacrylate,dimethylol-tricyclodecane diacrylate, bisphenol A EO (ethylene oxide)adduct diacrylate, bisphenol A PO (propylene oxide) adduct diacrylate,hydroxypivalate neopentyl glycol diacrylate, propoxylated neopentylglycol diacrylate, alkoxylated dimethyloltricyclodecane diacrylate andpolytetramethylene glycol diacrylate, trimethylolpropane triacrylate, EOmodified trimethylolpropane triacrylate, tri(propyleneglycol)triacrylate, caprolactone modified trimethylolpropanetriacrylate, pentaerythritol triacrylate, pentaerithritol tetraacrylate,pentaerythritolethoxy tetraacrylate, dipentaerythritol hexaacrylate,ditrimethylolpropane tetraacrylate, glycerinpropoxy triacrylate,caprolactam modified dipentaerythritol hexaacrylate, N-vinylamide suchas N-vinylcaprolactam or N-vinylformamide; or acrylamide or asubstituted acrylamide such as acryloylmorpholine; and aminofunctionalized polyetheracrylates such as described in U.S. Pat. No.6,300,388 (AGFA).

Furthermore, methacrylates corresponding to the above-mentionedacrylates may be used with these acrylates. Of the methacrylates,methoxypolyethylene glycol methacrylate, methoxytriethylene glycolmethacrylate, 4-(vinyloxy)butylmethacrylate, vinyl ether acrylates suchas described in U.S. Pat. No. 6,310,115 (AGFA), hydroxyethylmethacrylate, phenoxyethyl methacrylate, cyclohexyl methacrylate,tetraethylene glycol dimethacrylate, and polyethylene glycoldimethacrylate are preferred due to their relatively high sensitivityand higher adhesion to an ink-receiver surface.

Furthermore, the inkjet inks may also contain polymerizable oligomers.Examples of these polymerizable oligomers include epoxy acrylates,aliphatic urethane acrylates, aromatic urethane acrylates, polyesteracrylates, and straight-chained acrylic oligomers.

Norrish Type II Initiators

A Norrish type II initiator is a catalyst, usually called aphoto-initiator, for initiating the polymerization reaction. Thephoto-initiator requires less energy to activate than the monomers andoligomers to form the polymer.

The photo-initiator absorbs light and is responsible for the productionof free radicals or cations. Free radicals or cations are high-energyspecies that induce polymerization of monomers, oligomers and polymersand with polyfunctional monomers and oligomers thereby also inducingcross-linking.

A preferred amount of initiator is 1-50 wt % of the total ink weight,and more preferably 1 to 25 wt % of the total ink weight.

Irradiation with actinic radiation may be realized in two steps bychanging wavelength or intensity. In such cases it is preferred to use 2types of initiator together.

A preferred Norrish type II-initiator is selected from the groupconsisting of benzophenones, thioxanthones, 1,2-diketones andanthraquinones.

Suitable Norrish type II-initiators are disclosed in CRIVELLO, J. V., etal. VOLUME III: Photoinitiators for Free Radical Cationic & AnionicPhotopolymerization. 2ndth edition. Edited by BRADLEY, G. London, UK:John Wiley and Sons Ltd, 1998. p. 287-294.

Colorants

Colorants may be dyes, but are preferably pigments or a combinationthereof. Organic and/or inorganic pigments may be used.

The pigment particles should be sufficiently small to permit free flowof the ink through the inkjet printing device, especially at theejecting nozzles which usually have a diameter ranging from 10 μm to 50μm. The particle size influences also the pigment dispersion stability.It is also desirable to use small particles for maximum colour strength.The particles of the pigment dispersed in the inkjet ink should have aparticle size of less than 10 μm, preferably less than 3 μm, and mostpreferably less than 1μm. The average particle size of pigment particlesis preferably 0.05 to 0.5 μm.

Suitable pigments include as red or magenta pigments: Pigment Red 3, 5,19, 22, 31, 38, 43, 48: 1, 48: 2, 48: 3, 48: 4, 48: 5, 49: 1, 53: 1, 57:1, 57: 2, 58: 4, 63: 1, 81, 81: 1, 81: 2, 81: 3, 81: 4, 88, 104, 108,112, 122, 123, 144, 146, 149, 166, 168, 169, 170, 177, 178, 179, 184,185, 208, 216, 226, 257, Pigment Violet 3, 19, 23, 29, 30, 37, 50, and88; as blue or cyan pigments: Pigment Blue 1, 15, 15: 1, 15: 2, 15: 3,15: 4, 15: 6, 16, 17-1, 22, 27, 28, 29, 36, and 60; as green pigments:Pigment green 7, 26, 36, and 50; as yellow pigments: Pigment Yellow 1,3, 12, 13, 14, 17, 34, 35, 37, 55, 74, 81, 83, 93, 94, 95, 97, 108, 109,110, 128, 137, 138, 139, 153, 154, 155, 157, 166, 167, 168, 177, 180,185, and 193; as white pigment: Pigment White 6, 18, and 21.

Furthermore, the pigment may be chosen from those disclosed by HERBST,W, et al. Industrial Organic Pigments, Production, Properties,Applications. 2nd edition. VCH, 1997.

Most preferred pigments are Pigment Yellow 1, 3, 128, 109, 93, 17, 14,10, 12, 13, 83, 65, 75, 74, 73, 138, 139, 154, 151, 180, 185; PigmentRed 122, 22, 23, 17, 210, 170, 188, 185, 146, 144, 176, 57:1, 184, 202,206, 207; Pigment Blue 15:3, Pigment Blue 15:2, Pigment Blue 15:1,Pigment Blue 15:4, Pigment Blue 15:6, Pigment Blue 16 and Pigment Violet19.

Carbon black is usually used as the colouring material in black ink.Suitable black pigment materials include carbon blacks such as PigmentBlack 7 (e.g. Carbon Black MA8™ from MITSUBISHI CHEMICAL), Regal™ 400R,Mogul™ L, Elftex™ 320 from CABOT Co., or Carbon Black FW18, SpecialBlack 250, Special Black 350, Special Black 550, Printex™ 25, Printex™35, Printex™ 55, Printex™ 90, Printex™ 150T from DEGUSSA. Additionalexamples of suitable pigments are disclosed in U.S. Pat. No. 5,538,548(BROTHER).

The pigment is present in the range of 0.1 to 10 wt %, preferably in therange 1 to 5 wt % based on the total weight of the radiation curableinkjet ink.

Dyes suitable for the radiation curable inkjet ink include direct dyes,acidic dyes, basic dyes and reactive dyes.

Suitable direct dyes for the radiation curable inkjet ink include:

-   -   C.I. Direct Yellow 1, 4, 8, 11, 12, 24, 26, 27, 28, 33, 39, 44,        50, 58, 85, 86, 100, 110, 120, 132, 142, and 144    -   C.I. Direct Red 1, 2, 4, 9, 11, 134, 17, 20, 23, 24, 28, 31, 33,        37, 39, 44, 47, 48, 51, 62, 63, 75, 79, 80, 81, 83, 89, 90, 94,        95, 99, 220, 224, 227 and 343    -   C.I. Direct Blue 1, 2, 6, 8, 15, 22, 25, 71, 76, 78, 80, 86, 87,        90, 98, 106, 108, 120, 123, 163, 165, 192, 193, 194, 195, 196,        199, 200, 201, 202, 203, 207, 236, and 237    -   C.I. Direct Black 2, 3, 7, 17, 19, 22, 32, 38, 51, 56, 62, 71,        74, 75, 77, 105, 108, 112, 117, and 154

Suitable acidic dyes for the radiation curable inkjet ink include:

-   -   C.I. Acid Yellow 2, 3, 7, 17, 19, 23, 25, 20, 38, 42, 49, 59,        61, 72, and 99    -   C.I. Acid Orange 56 and 64    -   C.I. Acid Red 1, 8, 14, 18, 26, 32, 37, 42, 52, 57, 72, 74, 80,        87, 115, 119, 131, 133, 134, 143, 154, 186, 249, 254, and 256    -   C.I. Acid Violet 11, 34, and 75    -   C.I. Acid Blue 1, 7, 9, 29, 87, 126, 138, 171, 175, 183, 234,        236, and 249    -   C.I. Acid Green 9, 12, 19, 27, and 41    -   C.I. Acid Black 1, 2, 7, 24, 26, 48, 52, 58, 60, 94, 107, 109,        110, 119, 131, and 155

Suitable reactive dyes for the radiation curable inkjet ink include:

-   -   C.I. Reactive Yellow 1, 2, 3, 14, 15, 17, 37, 42, 76, 95, 168,        and 175    -   C.I. Reactive Red 2, 6, 11, 21, 22, 23, 24, 33, 45, 111, 112,        114, 180, 218, 226, 228, and 235    -   C.I. Reactive Blue 7, 14, 15, 18, 19, 21, 25, 38, 49, 72, 77,        176, 203, 220, 230, and 235    -   C.I. Reactive Orange 5, 12, 13, 35, and 95    -   C.I. Reactive Brown 7, 11, 33, 37, and 46    -   C.I. Reactive Green 8 and 19    -   C.I. Reactive Violet 2, 4, 6, 8, 21, 22, and 25    -   C.I. Reactive Black 5, 8, 31, and 39

Suitable basic dyes for the radiation curable inkjet ink include:

-   -   C.I. Basic Yellow 11, 14, 21, and 32    -   C.I. Basic Red 1, 2, 9, 12, and 13    -   C.I. Basic Violet 3, 7, and 14    -   C.I. Basic Blue 3, 9, 24, and 25

Dyes can only manifest the ideal colour in an appropriate range of pHvalue. Therefore, the radiation curable inkjet ink preferably furthercomprises a pH buffer, such as potassium hydroxide (KOH).

Inhibitors

Suitable polymerization inhibitors include phenol type antioxidants,hindered amine light stabilizers, phosphor type antioxidants,hydroquinone monomethyl ether commonly used in (meth)acrylate monomers,and hydroquinone, t-butylcatechol, pyrogallol may also be used. Ofthese, a phenol compound having a double bond in molecules derived fromacrylic acid is particularly preferred due to its having apolymerization-restraining effect even when heated in a closed,oxygen-free environment. Suitable inhibitors are, for example,Sumilizer™ GA-80, Sumilizer™ GM and Sumilizer™ GS produced by SumitomoChemical Co., Ltd.

Since excessive addition of these polymerization inhibitors will lowerthe ink sensitivity to curing, it is preferred that the amount capableof preventing polymerization be determined prior to blending. The amountof a polymerization inhibitor is generally between 200 and 20,000 ppm ofthe total ink weight.

Resins

The radiation curable inkjet ink may further contain a resin, alsocalled a pigment stabilizer or dispersant, in order to obtain a stabledispersion of the pigment(s) in the inkjet ink.

The pigments may be added to the radiation curable inkjet ink as adispersion comprising a dispersant.

Suitable resins: petroleum type resins (e.g., styrene type, acryl type,polyester, polyurethane type, phenol type, butyral type, cellulose type,and rosin); and thermoplastic resins (e.g., vinyl chloride, vinylacetatetype). Concrete examples of these resins include acrylate copolymers,styrene-acrylate copolymers, acetalized and incompletely saponifiedpolyvinyl alcohol, and vinylacetate copolymers. Commercial resins areknown under the tradenames Solsperse™ 32000 and Solsperse™ 39000available from AVECIA, EFKA™ 4046 available from EFKA CHEMICALS BV,Disperbyk™ 168 available from BYK CHEMIE GMBH.

A detailed list of non-polymeric as well as some polymeric dispersantsis disclosed by MC CUTCHEON. Functional Materials, North AmericanEdition. Glen Rock, N.J.: Manufacturing Confectioner Publishing Co.,1990. p. 110-129.

Typically resins are incorporated at 2.5% to 200%, more preferably at50% to 150% by weight of the pigment.

Surfactants

The radiation curable inkjet ink may contain at least one surfactant.The surfactant(s) can be anionic, cationic, non-ionic, or zwitter-ionicand are usually added in a total quantity below 20 wt % based on thetotal ink weight and particularly in a total below 10 wt % based on thetotal ink weight.

A fluorinated or silicone compound may be used as a surfactant, however,a potential drawback is extraction by food from inkjet food packagingmaterial because the surfactant does not cross-link. It is thereforepreferred to use a copolymerizable monomer having surface-activeeffects, for example, silicone-modified acrylates, silicone modifiedmethacrylates, fluorinated acrylates, and fluorinated methacrylates.

Solvents

The radiation curable inkjet ink may contain as a solvent, water and/ororganic solvents, such as alcohols, fluorinated solvents and dipolaraprotic solvents, the solvent preferably being present in aconcentration between 10 and 80 wt %, particularly preferably between 20and 50 wt %, each based on the total weight of the radiation curableinkjet ink.

However, the radiation curable inkjet ink preferably does not contain anevaporable component, but sometimes, it can be advantageous toincorporate an extremely small amount of an organic solvent in such inksto improve adhesion to the ink-receiver surface after UV curing. In thiscase, the added solvent can be any amount in the range which does notcause problems of solvent resistance and VOC, and preferably 0.1-5.0 wt%, and particularly preferably 0.1-3.0 wt %, each based on the totalweight of the radiation curable inkjet ink

Suitable organic solvents include alcohol, aromatic hydrocarbons,ketones, esters, aliphatic hydrocarbons, higher fatty acids, carbitols,cellosolves, higher fatty acid esters. Suitable alcohols include,methanol, ethanol, propanol and 1-butanol, 1-pentanol, 2-butanol,t.-butanol. Suitable aromatic hydrocarbons include toluene, and xylene.Suitable ketones include methyl ethyl ketone, methyl isobutyl ketone,2,4-pentanedione and hexafluoroacetone. Also glycol, glycolethers,N-methylpyrrolidone, N,N-dimethylacetamid, N,N-dimethylformamid may beused.

Biocides

Suitable biocides for the radiation curable inkjet ink include sodiumdehydroacetate, 2-phenoxyethanol, sodium benzoate, sodiumpyridinethion-1-oxide, ethyl p-hydroxybenzoate and1,2-benzisothiazolin-3-one and salts thereof. A preferred biocide forradiation curable inkjet ink is Proxel™ GXL available from ZENECACOLOURS.

A biocide is preferably added in an amount of 0.001 to 3 wt %, morepreferably 0.01 to 1.00 wt. %, each based on the radiation curableinkjet ink.

Preparation of a Radiation Curable Inkjet Ink

A dispersion of colorant for use in the radiation curable inkjet ink maybe prepared by mixing, milling and dispersion of colorant and resin.Mixing apparatuses may include a pressure kneader, an open kneader, aplanetary mixer, a dissolver, and a Dalton Universal Mixer. Suitablemilling and dispersion apparatuses are a colloid mill, a high-speeddisperser, double rollers, a bead mill, a paint conditioner, and triplerollers. The dispersions may also be prepared using ultrasonic energy.

In the process of mixing, milling and dispersion, each process isperformed with cooling to prevent build up of heat, and as much aspossible under light conditions in which UV-light has been substantiallyexcluded.

The radiation curable inkjet ink may be prepared using separatedispersions for each colorant, or alternatively several pigments may bemixed and co-milled in preparing the dispersion.

EXAMPLES

The present invention will now be described in detail by way of Exampleshereinafter.

Measurement Methods

1. Curing Speed

The percentage of the maximum output of the lamp was taken as a measurefor curing speed, the lower the number the higher curing speed. A samplewas considered as fully cured at the moment scratching with a Q-tipcaused no visual damage.

2. Method of Extraction

A sample of 3 cm in diameter was taken from each coated and curedcurable composition. The sample was put in a beaker and extracted twicewith 2 ml acetonitrile using ultrasound. The beaker and the sample wererinsed with 5 ml acetonitrile and the acetonitrile fractions were pooledand filtered over a Millex 0.2 μm filter. 10 mg of the referencecompounds (the hyperbranched polymers or comparative compounds) weredissolved in 50 ml acetonitrile.

The samples were analyzed on a Alltime C185 μm HPLC column (Alltech)(150 mm×3.2 mm)

20 μL of the extraction samples and 5 μL of the reference compounds wereinjected. A step gradient elution was used using a mixture of 0.2 MK₂HPO₄ adjusted to pH=7 with H₃PO₄ and 40/60 H₂O/CH₃CN at the start,switching to 40/60 H₂O/CH₃CN after 11 minutes and to 10/90 H₂O/CH₃CNafter 19 minutes. The total peak area compared to the referencecompounds was taken as a measure for the amount co-initiator extracted.Benzophenone was determined separately in the same run. When the peaksoverlapped with benzophenone, the benzophenone peak area was subtractedfrom the total peak area to determine the concentration of theextractable co-initiators. This was calculated back to a percentage ofthe original amount of co-initiator in the curable composition.

3. Viscosity

The viscosity of the radiation curable composition was measured with aBrookfield DV-II+viscometer at 25° C. and shear rate 3 RPM.

Materials

All materials used in the following examples were readily available fromAldrich Chemical Co. (Belgium) unless otherwise specified. The “water”used in the examples was deionized water. The following materials wereused:

DPGDA™ is a difunctional acrylate monomer available from UCB.

Sartomer™ SR351 is a trifunctional acrylate monomer available from BASF

Irgacure™ 500 is a photo-initiator mixture available from CIBA SPECIALTYCHEMICALS.

All hyperbranched polyglycidols PG₈, PG₁₅, PG₁7, PG₃₃ and PG₃₆ areavailable from HYPERPOLYMERS GMBH, Freiburg, Germany

Quantacure™ EHA and Quantacure™ ITX available from RAHN AG.

PET is poly(ethylene) terephthalate. Unsubbed PET substrate with on thebackside an anti-blocking layer with anti-static properties availablefrom AGFA-GEVAERT as P125C PLAIN/ABAS.

Example 1

This example illustrates the synthesis of a polymeric co-initiator witha hyperbranched polyglycidol core. The polymeric co-initiators CI-1 toCI-5 prepared, are represented by generalized formula CI-A.Generalized Formula CI-A

The hyperbranched polyglycidols selected for this example had threedifferent molecular weights:

-   -   PG₈ : a hyperbranched polyglycidol with 8 hydroxyl groups on        average;    -   PG₁₅: a hyperbranched polyglycidol with 15 hydroxyl groups on        average; and    -   PG₃₆: a hyperbranched polyglycidol with 36 hydroxyl groups on        average.        Synthesis of Polymeric Co-Initiator CI-1        (PG₁₅DMBA_(4.1)Piv_(10.9))

2 g of the hyperbranched polyglycidol PG₁₅ was dissolved in 50 mLpyridine. The solution was flushed with nitrogen. 0.3 equivalentsrelative to the hydroxyl groups of 4-dimethylamino-benzoylchloride wereadded and the reaction mixture was heated to 100° C. for 16 hours. Thereaction mixture was allowed to cool down to room temperature and 0.9equivalents relative to the hydroxyl groups of pivaloyl chloride wereadded. The mixture was heated to 70° C. for 16 hours. After 16 hours, 2mL of water was added and the solvent was removed under reducedpressure. The oily residue was dissolved in chloroform and the organicphase was extracted twice with a 5% solution of oxalic acid, twice withdeionized water, twice with a 10% NaOH solution and three times withdeionized water. The organic phase was dried over Na₂SO₄ and evaporatedunder reduced pressure. The isolated polymer was dried under vacuum at40° C. for 16 hours. The structure of the isolated polymer was confirmedby ¹H-NMR.

The polymeric co-initiator CI-1 was a hyperbranched polyglycidol with 15hydroxyl end groups on average, where 4.1 hydroxyl groups on averagewere acylated with 4-dimethylamino-benzoic acid and 10.9 hydroxyl groupson average were acylated with pivalic acid. The polymeric co-initiatorCI-1 had a numeric average molecular weight of 2500.

Synthesis of Polymeric Co-Initiator CI-2 (PG₃₆DMBA₉Piv₂₇)

The polymeric co-initiator CI-2 was prepared in the same manner aspolymeric co-initiator CI-1 except that PG₃₆ was used.

The polymeric co-initiator CI-2 was a hyperbranched polyglycidol with 36hydroxyl end groups on average, where 9 hydroxyl groups on average wereacylated with 4-dimethylamino-benzoic acid and 27 hydroxyl groups onaverage were acylated with pivalic acid. The polymeric co-initiator CI-2had a numeric average molecular weight of 6200.

Synthesis of Polymeric Co-Initiator CI-3 (PG₈DMBA4.9Piv_(3.1))

The polymeric co-initiator CI-3 was prepared in the same manner asco-initiator CI-1 except that PG₈ was used and that 0.5 equivalents4-dimethylamino-benzoylchloride and 0.7 equivalents pivaloyl chloriderelative to the hydroxyl groups of the hyperbranched polyglycidols wasused.

The obtained polymeric co-initiator CI-3 was a hyperbranchedpolyglycidol with 8 hydroxyl end groups on average, where 4.9 hydroxylgroups on average were acylated with 4-dimethylamino-benzoic acid and3.1 hydroxyl groups on average were acylated with pivalic acid. Thepolymeric co-initiator CI-3 had a numeric average molecular weight of1500.

Synthesis of Polymeric Co-Initiator CI-4 (PG₁₅DMBA_(7.5)Piv_(7.5))

The polymeric co-initiator CI-4 was prepared in the same manner asco-initiator CI-1 except that 0.5 equivalents4-dimethylamino-benzoylchloride and 0.7 equivalents pivaloyl chloriderelative to the hydroxyl groups of the hyperbranched polyglycidols wasused.

The obtained polymeric co-initiator CI-4 was a hyperbranchedpolyglycidol with 15 hydroxyl end groups on average, where 7.5 hydroxylgroups on average were acylated with 4-dimethylamino-benzoic acid and7.5 hydroxyl groups on average were acylated with pivalic acid. Thepolymeric co-initiator CI-4 had a numeric average molecular weight of2760.

Synthesis of Polymeric Co-Initiator CI-5 (PG₃₆DMBA_(16.8)Piv_(19.2))

The polymeric co-initiator CI-5 was prepared in the same manner asco-initiator CI-2 except that 0.5 equivalents4-dimethylamino-benzoylchloride and 0.7 equivalents pivaloyl chloriderelative to the hydroxyl groups of the hyperbranched polyglycidols wasused.

The polymeric co-initiator CI-5 was a hyperbranched polyglycidol with 36hydroxyl end groups on average, where 16.8 hydroxyl groups on averagewere acylated with 4-dimethylamino-benzoic acid and 19.2 hydroxyl groupson average were acylated with pivalic acid. The polymeric co-initiatorCI-5 had a numeric average molecular weight of 6700.

Example 2

This example illustrates the effectiveness of the polymericco-initiators in radiation curable compositions.

The comparative radiation curable composition COMP-1 and the inventiveradiation curable compositions INV-1 to INV-10 were prepared accordingto Table 6. The weight % (wt %) was based on the total weight of theradiation curable composition. TABLE 6 wt % of: COMP1 INV1 INV2 INV3INV4 INV5 INV6 INV7 INV8 INV9 INV10 DPGDA 41 52 52 44 44 50 50 42 42 4242 Sartomer ™ SR351 41 30 30 30 30 30 30 30 30 30 30 Irgacure ™ 500 1010 — 10 — 10 — 10 — 10 — Benzophenone — — 10 — 10 — 10 — 10 — 10Quantacure ™ EHA 8 — — — — — — — — — — CI-1 — — — 16 16 — — — — — — CI-2— — — — — — — 18 18 — — CI-3 — 8 8 — — — — — — — — CI-4 — — — — — 10 10— — — — CI-5 — — — — — — — — — 18 18

The comparative radiation curable composition COMP-1 and the inventiveradiation curable compositions INV-1 to INV-10 were coated on anunsubbed 100 μm PET substrate using a bar coater and a 10 μm wired bar.Each coated layer was cured using a Fusion DRSE-120 conveyer, equippedwith a Fusion VPS/I600 lamp (D-bulb), which transported the samplesunder the UV lamp on a conveyer belt at a speed of 20 m/min. The curingspeed was determined for the comparative radiation curable compositionCOMP-1 and the inventive radiation curable compositions INV-1 to INV-10.The results are summarized in Table 7. TABLE 7 Radiation curableSensitivity composition % of maximum output COMP-1 80 INV-1 45 INV-2 50INV-3 40 INV-4 100 INV-5 50 INV-6 80 INV-7 50 INV-8 65 INV-9 40  INV-1050

Table 7 shows that all inventive radiation curable compositions have acomparable to higher curing speed compared to the comparative radiationcurable composition COMP-1 with a state of the art commercialco-initiator.

Example 3

This example illustrates that the polymeric co-initiators according tothe present invention are not likely to be extracted by food when foodpackaging materials are printed upon with a radiation curable inkcontaining such a polymeric co-initiator.

Radiation curable compositions were prepared according to Table 8 usingthe polymeric co-initiators synthesized in Example 1. The weight % (wt%) was based on the total weight of the radiation curable composition.TABLE 8 wt % of COMP-2 INV-11 INV-12 INV-13 DPGDA 53 52 50 42 Sartomer ™SR351 30 30 30 30 Benzophenone 10 10 10 10 Quantacure ™ EHA  7 — — —CI-2 — — 10 — CI-3 —  8 — — CI-4 — — — 18

The comparative radiation curable composition COMP-2 and the inventiveradiation curable compositions INV-11 to INV-13 were coated on anunsubbed 100 μm PET substrate using a bar coater and a 10 μm wired bar.Each coated layer was cured using a Fusion DRSE-120 conveyer, equippedwith a Fusion VPS/I600 lamp (D-bulb), which transported the samplesunder the UV lamp on a conveyer belt at a speed of 20 m/min. Theviscosity and the amount of initiator, that could be extracted fromcoated and cured samples of the comparative radiation curablecomposition COMP-2 and the inventive radiation curable compositionsINV-11 to INV-13, were determined. The results are summarized in Table9. TABLE 9 Coated & cured sample Viscosity of composition (mPa · s) %co-initiator extracted COMP-2 20 47 INV-11 25 17 INV-12 34 29 INV-13 6329

The results in Table 9 clearly demonstrate the reduced extractability ofpolymeric co-initiators. All the inventive radiation curablecompositions INV-11 to INV-13 have a viscosity smaller than 100 mpa.s,which is a requirement for most radiation curable inkjet inks.

Example 4

This example illustrates that hyperbranched polymeric co-initiators canbe further derivatized with a compatibilizing group and that they remaineffective polymeric co-initiators in radiation curable compositions.

The prepared polymeric co-initiators CI-6 to CI-8 are represented bygeneralized formula CI-B.

Generalized formula CI-B

wherein,

-   -   PG represents a hyperbranched polyglycidol core    -   x represents the average number of terminal hydroxyl groups in        the starting polyglycidol

The polymeric co-initiators CI-6 to CI-8 were prepared according toTable 10, which mentions the ratio of the different groups acylated ontoeach starting polyglycidol core. TABLE 10 Co-initiator X DMBA MEEA AcGeneral formula CI-6 8 3.4 3.5 1.1 PG₈DMBA_(3.4)MEEA_(3.5)Ac_(1.1) CI-717 3.4 8.8 4.8 PG₁₇DMBA_(3.4)MEEA_(8.8)Ac_(4.8) CI-8 33 6.6 16.5 9.9PG₃₃DMBA_(6.6)MEEA_(16.5)Ac_(9.9)

The synthesis is exemplified for the polymeric co-initiator CI-7. 3.45 g(2.84 mmol) of PG₁₇, 2.95 mL (19.3 mmol) of MEEA and 0.96 g (4.83 mmol)of p-toluenesulfonic acid monohydrate were added into a 100 mL one-neckflask equipped with a Dean-Stark and a condenser. Then 40 mL of toluenewas added and the mixture was heated to 136° C. and stirred for 3 hours,while water was azeotropically removed. Then the solvent was removedunder vacuum. At the same time a solution of 4.79 g (29.0 mmol) of4-dimethylaminobenzoic acid and 4.71 g (29.0 mmol) of1,1′-carbonyidiimidazole (CDI) in 40 mL of THF was stirred at roomtemperature for 3 hours. Then this solution was added to the flaskcontaining the MEEA partially modified PG. After the mixture wasrefluxed overnight, 2.74 mL (29.0 mmol) of acetic anhydride was added tomodify the residual hydroxyl groups of PG. The solution was refluxed for6 hours, before water was added to destroy the residual aceticanhydride. After removing most of the volatile compounds under reducedpressure, the residue was dissolved in chloroform. The mixture waswashed twice with 5% of oxalic acid aq, three times with deionizedwater, twice with 10% of NaOH aq and several times by NaCl aq untilpH=7. After removing the solvent, the residual water was removed byazeotropical. distillation with toluene. After filtration, most of thetoluene was removed and the residue was kept at 40° C. in a vacuum ovenovernight.

The co-initiators CI-6 and CI-8 were prepared in the same manner andanalyzed with ¹H NMR (CDCl₃): d=0.77, 1.32 (TMP core of PG); 2.01(CH₃COO—); 2.99 ((CH₃)₂N—); 3.07-5.52 (protons of PG and MEEA moieties);6.58 and 7.82 (proton of aromatic ring).

The synthesized polymeric co-initiators displayed properties asdisclosed by Table 11. TABLE 11 Co-initiator M_(n) Yield CI-6 1627 41%CI-7 3326 63% CI-8 6348 47%

The comparative radiation curable composition COMP-3 and inventiveradiation curable compositions INV-14 to INV-16 were prepared accordingto Table 12. The initiator/co-initiator molar ratio was kept constant.The weight % (wt %) was based on the total weight of the radiationcurable composition. TABLE 12 wt % COMP-3 INV-14 INV-15 INV-16 DPGDA50.0 46.5 37.0 38.0 Sartomer ™ SR351 40.0 40.0 40.0 40.0 Quantacure ™ITX 5.0 5.0 5.0 5.0 Quantacure ™ EHA 5.0 — — — CI-6 — 8.5 — — CI-7 — —18.0 — CI-8 — — — 17.0

The comparative radiation curable composition COMP-3 and the inventiveradiation curable compositions INV-14 to INV-16 were coated on anunsubbed 100 μm PET substrate using a bar coater and a 10 μm wired bar.Each coated layer was cured using a Fusion DRSE-120 conveyer, equippedwith a Fusion VPS/I600 lamp (D-bulb), which transported the samplesunder the UV lamp on a conveyer belt at a speed of 20 m/min. The curingspeed was determined for the comparative radiation curable compositionCOMP-3 and the inventive radiation curable compositions INV-14 toINV-16. The results are summarized in Table 13. TABLE 13 Radiationcurable Sensitivity composition % of maximum output COMP-3 50 INV-14 100INV-15 40 INV-16 50

Table 13 shows that all of the samples prepared with the inventiveradiation curable compositions INV-14 to INV-16 have a comparable tohigher curing speed compared to the comparative radiation curablecomposition COMP-3 with a state of the art commercial co-initiator.

Example 5

In this example the effectiveness in a radiation curable composition ofa hyperbranched polymeric co-initiator further derivatized with acompatibilizing group is compared with that of a corresponding compoundof low molecular weight.

The prepared polymeric co-initiators CI-9 to CI-13 are represented bygeneralized formula CI-C.

Generalized formula CI-C

wherein,

-   -   PG represents a hyperbranched polyglycidol core    -   x represents the average number of terminal hydroxyl groups in        the starting polyglycidol

The polymeric co-initiators CI-9 to CI-13 were prepared according toTable 14, which mentions the ratio of the different groups acylated ontoeach starting polyglycidol core. TABLE 14 Co-initiator X PPA MEEA AcGeneral formula CI-9 8 4.1 3.6 0.3 PG₈PPA_(4.1)MEEA_(3.6)Ac_(0.3) CI-1017 5.3 11.2 0.5 PG₁₇PPA_(5.3)MEEA_(11.2)Ac_(0.5) CI-11 17 7.1 8.2 1.7PG₁₇PPA_(7.1)MEEA_(8.2)Ac_(1.7) CI-12 33 10.0 22.4 0.6PG₃₃PPA₁₀MEEA_(22.4)Ac_(0.6) CI-13 33 13.9 15.8 3.3PG₃₃PPA_(13.9)MEEA_(15.8)Ac_(3.3)

The synthesis is exemplified for the polymeric co-initiator CI-10. 3.66g (3.0 mmol) of PG₁₇ (M_(n)=1214 g/mol⁻¹, M_(w)/M_(n)=1.6), 2.41 g (15.3mmol) of 1-piperidinepropionic acid (PPA), 2.34 mL (15.3 mmol) of2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEA) and 3.90g (20.4mmol) ofp-toluenesulfonic acid monohydrate were added into a 100 mL one-neckflask equipped with a Dean-Stark and a condenser. 40 mL of toluene wasadded and the mixture was heated to 136° C. and stirred for 3 hours,while water was azeotropically removed. Then 4.68 mL (30.6 mmol) of MEEAwas added and the mixture was heated to 136° C. and stirred for anadditional 6 hours. Subsequently 1.76 mL (30.6 mmol) of acetic acid wasadded, the mixture was stirred overnight under the same reactioncondition. After removing most of the solvent under reduced pressure,the residue was dissolved in chloroform. The mixture was washed twicewith 10% of NaOH aq and several times with NaCl aq until pH=7. Afterremoving the solvent, residual water was removed by azeotropicaldistillation with toluene. After filtration, most of the toluene wasremoved and the residue was kept at 40° C. in a vacuum oven overnight.

The co-initiators CI-9 and CI-11 to CI-13 were prepared in the samemanner and analyzed with ¹H NMR (CDCl₃): δ=0.77, 1.32 (TMP core of PG);1.14-1.64(β and γ CH₂ in piperidine ring); 1.98 (CH₃COO—); 2.13-2.66 (αCH₂ in piperidine ring, —NCH₂CH₂COO—); 3.0-5.27 (protons of PG and MEEAmoieties).

The synthesized polymeric co-initiators displayed properties asdisclosed by Table 15. TABLE 15 Co-initiator M_(n) Yield CI-9  1680 65%CI-10 3766 72% CI-11 3587 69% CI-12 7321 78% CI-13 6922 71%

A corresponding compound LI-1 of low molecular weight was synthesizedaccording to the reaction:

11 g of 2-(2-ethoxyethoxy)ethylacrylate was added dropwise to a solutionof 5 g piperidine in 30 ml ethanol. Upon addition of the acrylate, thetemperature rose to 50° C. The reaction was allowed to continue for 1hour at room temperature. Based on TLC-analysis, the conversion was asgood as quantitative (eluent CH₂Cl₂/MeOH: 95/5). The solvent was removedunder reduced pressure and the compound was dried under vacuum. Thecompound LI-1 was sufficiently pure for direct use.

The comparative radiation curable composition COMP-4 and inventiveradiation curable compositions INV-17 to INV-21 were prepared accordingto Table 16. The initiator/co-initiator molar ratio was kept constant.The weight % (wt %) was based on the total weight of the radiationcurable composition. TABLE 16 COMP- wt % 4 INV-17 INV-18 INV-19 INV-20INV-21 DPGDA 50.0 47.5 42.0 46.0 41.5 46.0 Sartomer ™ 40.0 40.0 40.040.0 40.0 40.0 SR351 Quantacure ™ 5.0 5.0 5.0 5.0 5.0 5.0 ITX Compound5.0 — — — — — LI-1 CI-9 — 7.5 — — — — CI-10 — — 13.0 — — — CI-11 — — —9.0 — — CI-12 — — — — 13.5 — CI-13 — — — — — 9.0

The comparative radiation curable composition COMP-4 and inventiveradiation curable compositions INV-17 to INV-21 were coated on anunsubbed 100 μm PET substrate using a bar coater and a 10 μm wired bar.Each coated layer was cured using a Fusion DRSE-1 20 conveyer, equippedwith a Fusion VPS/I600 lamp (D-bulb), which transported the samplesunder the UV lamp on a conveyer belt at a speed of 20 m/min. The curingspeed was determined for the comparative radiation curable compositionCOMP-4 and inventive radiation curable compositions INV-17 to INV-21.The results are summarized in Table 17. TABLE 17 Coated & cured sampleof Sensitivity composition % of maximum output COMP-4 45 INV-17 60INV-18 45 INV-19 40 INV-20 40 INV-21 40

Table 17 shows that all of the inventive samples prepared with theradiation curable compositions INV-17 to INV-21 have a comparable tohigher curing speed compared to the sample prepared from the comparativeradiation curable composition COMP-4 with a corresponding co-initiatorLI-1 of low molecular weight.

Having described in detail preferred embodiments of the currentinvention, it will now be apparent to those skilled in the art thatnumerous modifications can be made therein without departing from thescope of the invention as defined in the following claims.

1. A polymeric co-initiator comprising a hyperbranched polymer core withat least one co-initiating functional group as an end group.
 2. Apolymeric co-initiator according to claim 1, wherein said at least oneco-initiating functional group is a co-initiating functional groupselected from the group consisting of a thiol, an aromatic amine and analiphatic amine.
 3. A polymeric co-initiator according to claim 1,wherein said at least one co-initiating functional group is aco-initiating functional group selected from the group consisting oftertiary amines, heterocyclic thiols and 4-dialkylamino-benzoic acid and4-dialkylamino-benzoic acid derivatives.
 4. A polymeric co-initiatoraccording to claim 1, wherein said polymeric co-initiator has at leastfive co-initiating functional groups as end groups on the hyperbranchedpolymer core.
 5. A polymeric co-initiator according to claim 1, whereinsaid hyperbranched polymer core has at least one other functional groupas an end group.
 6. A polymeric co-initiator according to claim 5,wherein said one other functional group is a compatibilizing group toimprove the compatibility of the polymeric co-initiator with a radiationcurable composition.
 7. A polymeric co-initiator according to claim 1,wherein said hyperbranched polymer core has a polydispersity hd w/M_(n)smaller than
 3. 8. A polymeric co-initiator according to claim 1,wherein said hyperbranched polymer core is a polyglycidol.
 9. A processfor manufacturing a polymeric co-initiator, comprising the steps of: a)providing a hyperbranched polymer core, and b) attaching at least oneco-initiator or co-initiator derivative to said hyperbranched polymercore as an end group.
 10. A process for manufacturing a polymericco-initiator according to claim 9, wherein said hyperbranched polymercore has a polydispersity M_(w)/M_(n) smaller than
 3. 11. A process formanufacturing a polymeric co-initiator according to claim 9, whereinsaid hyperbranched polymer core is a polyglycidol.
 12. A process formanufacturing a polymeric co-initiator according to claim 9, whereinsaid at least one co-initiator or co-initiator derivative is selectedfrom the group consisting of: